1. Field of the Invention
The present invention relates to an anti-theft device for motor vehicles which are equipped with an electronic engine control unit.
2. Description of the Prior Art
It is known to equip motor vehicles with electronic engine controls. These controls scan the environmental factors and operating factors and control the engine functions. Furthermore, these engine controls can be used to monitor conditions and indicate faulty functioning. These engine control units are quite often standardized modules for particular vehicles and/or models, wherein a particular module is supplied as a ready made component for each vehicle model. These modules are usually provided in the form of a closed steel casing, which can be mounted for easy replacement in or on the vehicle. To connect the module, there is usually provided a multipolar plug connection, in which the signalling, measuring and control leads (and possibly other leads) align, and which serves to provide a plug connection with the replaceable module.
In the case of an anti-theft device for motor vehicles, special care must be taken to ensure that unauthorized starting of the vehicle is prevented to provide the greatest possible security. It has been shown tht it is much more important to prevent the vehicle from being driven away without authorization than it is to indicate an unauthorized start by acoustic and/or optical signals. Experience has shown that the skills of the car thieves to overcome security devices increase in parallel with the technical improvements made to such security devices. For a car thief, it is of major importance to overcome a security device in the shortest possible time. There is, therefore, a great demand for anti-theft devices, which, on the one hand, are compatible with the normal vehicle operation, while, on the other hand, the time taken to overcome them, if this is at all possible, is lengthy.
A security measure may be provided by switching off any provided electronic engine control unit. Such switching may be undertaken from outside in lockable manner. After switching off the electronic engine control unit, it is not possible to start up the vehicle. For unauthorized starting, it would be necessary to switch on again, in the module, the contact breaker circuit which is installed in the casing and which can be operated and locked from the outside. A simple switching can be prevented by known security measures, such as, for example, a security key or coded switch.
It is known that thefts of high quality vehicles are carried out in a professional manner. With a well directed professional action, switching off the described security device could be achieved by thieves obtaining the commercially available modules of the electronic engine control units for each specific vehicle model, and, when attempting a theft, use these to replace the switched off module. However, such a replacement automatically requires the removal of the multipolar plug connection from the module. From published German Patent Application No. 30 45 345, an anti-theft device for vehicles is already known, which includes a switch that interrupts an essential function of the engine, and that can be switched on by an operating device located inside the vehicle. The operating device is a switch mechanism on which various number combinations can be set. A decoder is attached to an electrical component of the engine which is essential to the functioning, and this decoder is connected by at least one electric lead to the switch mechanism and only produces an output signal when a specific specified number combination is set on the switch mechanism. This output signal of the decoder closes a contact breaker in a lead of this component.
From U.S. Patent No. 3,876,884, an anti-theft device is known which is safeguarded by the ignition key. With this known system, the ignition is designed so that a capacitive discharge ignition circuit can be connected to the induction ignition circuit. A commutator, which can be operated by the ignition key, is mounted on the said discharge ignition circuit.